University of Amsterdam, Cognitive Neuroscience Group, Department of Psychology, and University of Amsterdam Amsterdam Center for the Study of Adaptive Control in Brain and Behavior, Department of Psychology

K. Richard Ridderinkhof

University of Amsterdam, Amsterdam Center for the Study of Adaptive Control in Brain and Behavior, Department of Psychology

Johannes J. Fahrenfort

University of Amsterdam, Cognitive Neuroscience Group, Department of Psychology, and University of Amsterdam, Amsterdam Center for the Study of Adaptive Control in Brain and Behavior, Department of Psychology

Victor A. F. Lamme

University of Amsterdam, Cognitive Neuroscience Group, Department of Psychology, Netherlands, and Institute for Neuroscience, part of the Royal Netherlands Academy of Arts and Sciences

To obtain an understanding of the function of awareness, we need to know which cognitive functions are linked to conscious experience and which are not. We studied whether an unconscious — invisible- stimulus could trigger inhibitory processes. Inhibition is a high-level cognitive control function, in part mediated by the frontal lobes and commonly associated with consciousness. We developed a masked Go/No-Go paradigm, in which participants had to respond as fast as possible to a Go signal, but were instructed to withhold their response when they perceived a No-Go signal, preceding the Go-signal. In our version of this paradigm, the Go signal also functioned as a metacontrast mask, leading to undetectable No-Go signals at short SOAs, and perfectly visible No-Go signals at longer SOAs. During this task, EEG was measured to track the fate of masked No-Go signals in the brain. Behaviorally, masked No-Go signals sometimes triggered response inhibition to the level of complete response termination, as well as yielded a slow-down in the speed of responses that were not inhibited. In addition, EEG responses showed that masked No-Go signals elicit activation at fronto-central electrode sites where previous Go/No-Go studies found the largest inhibition related effects. Also, the amount of slowdown in individual subjects strongly correlated with the strength of the fronto-central EEG activity. These findings show that inhibitory control can be initiated by unconscious events. This challenges traditional views concerning the proposed intimate relationship between awareness and cognitive control and extends the limits of unconscious information processing.